The present invention relates to phosphorescent organic electroluminescent devices which, by observing certain relative energy levels of the materials in the emitting layer, exhibit an emission which is shifted to longer wavelength or mixed emission comprising the emission of the phosphorescent emitter and an emission which is shifted to longer wavelength.
The structure of organic electroluminescent devices (OLEDs) in which organic semiconductors are employed as functional materials is described, for example, in U.S. Pat. No. 4,539,507, U.S. Pat. No. 5,151,629, EP 0676461 and WO 98/27136. A development in the area of organic electroluminescent devices are phosphorescent OLEDs. These have significant advantages compared with fluorescent OLEDs owing to the higher achievable efficiency.
The technical object on which the present invention is based consists in providing a phosphorescent organic electroluminescent device in which the emission colour and the width of the emission band can be varied or adjusted specifically.
In accordance with the prior art, electron-conducting materials, inter alia ketones (for example in accordance with WO 2004/093207 or WO 2010/006680) or triazine derivatives (for example in accordance with WO 2010/015306), or hole-conducting materials, inter alia triarylamines or carbazole derivatives, are used as matrix materials for phosphorescent emitters.
In accordance with the prior art, the phosphorescent emitters used are furthermore, in particular, iridium and platinum complexes, which usually have bidentate ligands which are coordinated to the metal via a carbon atom and a nitrogen atom. An example of such phosphorescent emitters is tris(phenylpyridyl)iridium(III).
The prior art (for example in accordance with WO 2010/086089 or the unpublished application EP 10006208.2) additionally discloses metal complexes with imidazoisoquinoline and derivatives as ligands. Furthermore, the prior art (WO 2007/095118) discloses metal complexes with imidazo-phenanthridine or diimidazoquinazoline and derivatives as ligands. Many of these metal complexes emit blue or blue-green light.
Surprisingly, it has been found that the emission colour of an organic electroluminescent device can be shifted selectively over a broad range if certain physical parameters are observed for the choice of the phosphorescent emitter and of the matrix material. The organic electroluminescent device here has very good efficiency and lifetime. Likewise, broad emission bands which are suitable for the generation of white emission are accessible in this way.
WO 2003/059015 discloses that white-emitting organic electroluminescent devices are accessible through the use of emitters which form aggregates. Two emitters are doped into an emitting layer here, where one of the emitters forms aggregates. The formation of aggregates is highly dependent on the concentration of the emitters, which suggests aggregate formation between the emitters. The aggregate here has a broad emission band. For this aggregate formation, the use of planar compounds, for example platinum complexes, is suitable, but the use of complexes which have bulky substituents, such as, for example, tert-butyl groups, or the use of octahedral complexes is not.
The invention relates to an organic electroluminescent device comprising anode, cathode and at least one emitting layer which comprises at least one phosphorescent compound A and at least one compound B, characterised in that the following relationships (1) or the following relationships (2) apply to compounds A and B:T1(B)≧ΔE, where ΔE=|HOMO(A)|−|LUMO(B)|;  a)T1(A)≧ΔE, where ΔE=|HOMO(A)|−|LUMO(B)|;  b)|HOMO(B)|>|HOMO(A)|; and  c)|LUMO(B)|>|LUMO(A)|  d) (1)orT1(B)≧ΔE, where ΔE=|HOMO(B)|−|LUMO(A)|;  a)T1(A)≧ΔE, where ΔE=|HOMO(B)|−|LUMO(A)|;  b)|LUMO(A)|>|LUMO(B)|; and  c)|HOMO(A)|>|HOMO(B)|  d) (2)the following materials are excluded from the invention as compound B:
